8,411 research outputs found
Implications of a possible 23 day periodicity for binary black hole models in Mkn~501
We investigate the implications of a massive binary system in the centre of
the gamma-ray blazar Mkn~501 and show that the periodical behaviour recently
observed in the TeV and X-ray lightcurves may possibly be related to the
orbital motion of the relativistic jet emerging from the less massive black
hole. For the special relativistic jet properties inferred from emission
models, we derive an intrinsic orbital period of yrs and a
centre-of-mass distance of cm. If the binary is very
close with a separation of the order of that for which gravitational radiation
becomes dominant, we find a maximum primary mass of \sim 10^8 M_{\sun} and a
corresponding secondary mass in the range of \sim (4-42)\times 10^6 M_{\sun}
depending on the intrinsic jet properties. Such values are in line with the
black hole masses expected from merger scenarios.Comment: 6 pages, 1 figure; Springer A&A LaTeX; final version (small typos
corrected
A practical guide to computer simulations
Here practical aspects of conducting research via computer simulations are
discussed. The following issues are addressed: software engineering,
object-oriented software development, programming style, macros, make files,
scripts, libraries, random numbers, testing, debugging, data plotting, curve
fitting, finite-size scaling, information retrieval, and preparing
presentations.
Because of the limited space, usually only short introductions to the
specific areas are given and references to more extensive literature are cited.
All examples of code are in C/C++.Comment: 69 pages, with permission of Wiley-VCH, see http://www.wiley-vch.de
(some screenshots with poor quality due to arXiv size restrictions) A
comprehensively extended version will appear in spring 2009 as book at
Word-Scientific, see http://www.worldscibooks.com/physics/6988.htm
A possible black hole binary in Mkn 501
A simple binary model for Mkn~501 is considered under the assumption that the
TeV and X-ray periodicity of days, observed during the flaring state
in 1997, may be basically interpreted as a doppler-shifted flux modulation due
to the orbital motion of the relativistic jet. For the typical jet properties
inferred from emission models, we find an intrinsic orbital period of
yrs and a centre-of-mass distance of cm, the binary
thus being a very close system. If the binary separation corresponds to that at
which gravitational radiation becomes dominant, one may obtain a maximum
allowed primary mass of and a corresponding maximum
allowed secondary mass in the range of
assuming that gas accretion occurs on around the salpeter time scale.
Interestingly such values agree with the black hole masses expected from merger
scenarios.Comment: 4 pages, 2 figures; updated results of astro-ph/0005478; to appear in
the Proc. of the Heidelberg International Symposium on High Energy Gamma-Ray
Astronomy, Heidelberg, June 26-30, 2000, ed. by H.J. Voelk and F. Aharonian,
AIP Conf. Pro
Test particle acceleration by rotating jet magnetospheres
Centrifugal acceleration of charged test particles at the base of a rotating
jet magnetosphere is considered. Based on an analysis of forces we derive the
equation for the radial accelerated motion and present an analytical solution.
It is shown that for particles moving outwards along rotating magnetic field
lines, the energy gain is in particular limited by the breakdown of the
bead-on-the-wire approximation which occurs in the vicinity of the light
cylinder . The corresponding upper limit for the maximum Lorentz factor
for electrons scales , with the
magnetic field strength at , and is at most of the order of a
for the conditions regarded to be typical for BL Lac objects. Such
values suggest that this mechanism may provide pre-accelerated seed particles
which are required for efficient Fermi-type particle acceleration at larger
scales in radio jets.Comment: 4 pages, 1 figure; to appear in the Proc. of the Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy, Heidelberg, June
26-30, 2000, ed. by H.J. Voelk and F. Aharonian, AIP Conf. Pro
Domain walls and chaos in the disordered SOS model
Domain walls, optimal droplets and disorder chaos at zero temperature are
studied numerically for the solid-on-solid model on a random substrate. It is
shown that the ensemble of random curves represented by the domain walls obeys
Schramm's left passage formula with kappa=4 whereas their fractal dimension is
d_s=1.25, and therefore is NOT described by "Stochastic-Loewner-Evolution"
(SLE). Optimal droplets with a lateral size between L and 2L have the same
fractal dimension as domain walls but an energy that saturates at a value of
order O(1) for L->infinity such that arbitrarily large excitations exist which
cost only a small amount of energy. Finally it is demonstrated that the
sensitivity of the ground state to small changes of order delta in the disorder
is subtle: beyond a cross-over length scale L_delta ~ 1/delta the correlations
of the perturbed ground state with the unperturbed ground state, rescaled by
the roughness, are suppressed and approach zero logarithmically.Comment: 23 pages, 11 figure
Crossovers in the Two Dimensional Ising Spin Glass with ferromagnetic next-nearest-neighbor interactions
By means of extensive computer simulations we analyze in detail the two
dimensional Ising spin glass with ferromagnetic next-nearest-neighbor
interactions. We found a crossover from ferromagnetic to ``spin glass'' like
order both from numerical simulations and analytical arguments. We also present
evidences of a second crossover from the ``spin glass'' behavior to a
paramagnetic phase for the largest volume studied.Comment: 19 pages with 9 postscript figures also available at
http://chimera.roma1.infn.it/index_papers_complex.html. Some changes in
captions of figures 1 and
Effect of surface nanostructure on temperature programmed reaction spectroscopy: First-principles kinetic Monte Carlo simulations of CO oxidation at RuO2(110)
Using the catalytic CO oxidation at RuO2(110) as a showcase, we employ
first-principles kinetic Monte Carlo simulations to illustrate the intricate
effects on temperature programmed reaction spectroscopy data brought about by
the mere correlations between the locations of the active sites at a
nanostructured surface. Even in the absence of lateral interactions, this
nanostructure alone can cause inhomogeneities that cannot be grasped by
prevalent mean-field data analysis procedures, which thus lead to wrong
conclusions on the reactivity of the different surface species.Comment: 4 pages including 3 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Time Averaged VHE Spectrum of Mrk 421 in 2005
The blazar Mrk421 was observed independently, but contemporaneously, in 2005
at TeV energies by MAGIC, the Whipple 10m telescope, and by a single VERITAS
telescope during the construction phase of operations. A comparison of the time
averaged spectra, in what was a relatively quiescent state, demonstrates the
level of agreement between instruments. In addition, the increased sensitivity
of the new generation instruments, and ever decreasing energy thresholds,
questions how best to compare new observational data with archival results.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
Evaluation of a microbial muramidase supplementation on growth performance, apparent ileal digestibility, and intestinal histology of broiler chickens
The current study evaluated the effects of different inclusion levels of microbial muramidase (Muramidase 007, DSM Nutritional Products) on gastrointestinal functionality by determination of apparent ileal digestibility (AID) of nutrients, investigation of intestinal histomorphology, and quantification of resulting growth performance. Four maize-wheat-soybean experimental diets were produced without (C) and with different dosages of muramidase: low (L, 25,000 LSU(F)/kg), medium (M, 35,000 LSU(F)/kg), and high (H, 45,000 LSU(F)/kg); diets were fed to broilers for 35 d. At the end of the experiment, AID of ether extract (EE), crude protein (CP), Ca, and P were determined and samples of the mid-jejunum and -ileum were collected for histomorphological observations. Data were subjected to ANOVA analysis using the GLM procedure. Orthogonal polynomial contrasts were used to assess linear and quadratic effects of different levels of the muramidase. At the end of the trial, Muramidase 007 supplementation linearly increased body weight gain and decreased feed conversion ratio (FCR) (P ≤ 0.05). Adding the muramidase to broiler diets also linearly increased the European poultry efficiency factor (P ≤ 0.05). Inclusion of the muramidase in broiler diets linearly increased AID of CP, EE, and P (P ≤ 0.05), and the H group had a higher AID of EE and CP compared to C group (P ≤ 0.05). Microbial muramidase supplementation linearly increased ileal villus length to crypt depth ratio and decreased the number of ileal CD45 cells (P ≤ 0.05). Broilers fed M and H diets had fewer number of CD45 cells in the ileum compared to those in C group (P ≤ 0.05). In conclusion, the results of the present study demonstrated that inclusion of the microbial muramidase in broiler diets could increase AID of key nutrients and improve growth performance in broilers. Adding microbial muramidase to broiler diets can therefore be considered as an interesting prospect to improve gastrointestinal functionality. Biological mechanisms causing these improvements need to be studied further
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